Microchip Technology dsPIC30F - Page 89

© 2004 Microchip Technology Inc. DS70051C-page 4-5
Section 4. Program Memory
Program
Memory
4
4.3.1 Table Instruction Summary
A set of table instructions is provided to move byte or word-sized data between program space
and data space. The table read instructions are used to read from the program memory space
into data memory space. The table write instructions allow data memory to be written to the
program memory space.
The four available table instructions are listed below:
• TBLRDL: Table Read Low
• TBLWTL: Table Write Low
• TBLRDH: Table Read High
• TBLWTH: Table Write High
For table instructions, program memory can be regarded as two 16-bit word wide address spaces
residing side by side, each with the same address range as shown in Figure 4-3. This allows
program space to be accessed as byte or aligned word addressable, 16-bit wide, 64-Kbyte pages
(i.e., same as data space).
TBLRDL and TBLWTL access the LS Data Word of the program memory, and TBLRDH and
TBLWTH access the upper word. As program memory is only 24-bits wide, the upper byte from
this latter space does not exist, though it is addressable. It is, therefore, termed the ‘phantom’
byte.
Figure 4-3: High and Low Address Regions for Table Operations
Note: Detailed code examples using table instructions can be found in Section 5. “Flash
and EEPROM Programming”.
0
8
16
PC Address
0x000100
0x000102
0x000104
0x000106
23
00000000
00000000
00000000
00000000
Program Memory
‘Phantom’ Byte
(Read as ‘0’)
‘HIGH’ Table Address Range
‘LOW’ Table Address Range